JP7000197B2 - Concentration measuring method and concentration measuring device - Google Patents

Description

One aspect of the present invention relates to a concentration measuring method and a concentration measuring device for measuring the concentration of impurities in an object to be measured.

Conventionally, an apparatus for evaluating the characteristics of a measurement object such as a solar cell has been known (see, for example, Patent Document 1 below). This device has a pump light source that irradiates a pulsed pump light on the object to be measured, a probe light source that continuously irradiates the object to be measured with probe light, and a photodetector that detects the probe light radiated on the object to be measured in real time. It is composed of a device and a signal processing unit that processes the signal output from the photodetector. With such a configuration, it is possible to measure the state of occurrence and disappearance of carriers by measuring the time change of the amount of carriers.

Japanese Unexamined Patent Publication No. 2016-157780

With the conventional device as described above, it is possible to measure the time change of the carrier amount, but it is difficult to accurately measure the impurity concentration for the object to be measured whose impurity concentration is unknown.

Therefore, one aspect of the present invention has been made in view of such a problem, and it is an object of the present invention to provide a concentration measuring method and a concentration measuring device capable of accurately measuring the impurity concentration in a measurement object. ..

One embodiment of the present invention is a concentration measuring method for measuring the impurity concentration of an object to be measured, and irradiates the object to be measured with measurement light and stimulating light intensity-modulated with a modulation signal including a predetermined frequency. Irradiation step to be performed, an output step to detect the intensity of reflected light or transmitted light from the object to be measured and output a detection signal, and a frequency to detect the phase delay of the detection signal with respect to the modulated signal and set the phase delay to a predetermined value. Is provided, and an estimation step of estimating the impurity concentration of the object to be measured based on the frequency is provided.

Alternatively, another embodiment of the present invention is a concentration measuring device for measuring the impurity concentration of the object to be measured, wherein the first light source for generating the measurement light, the second light source for generating the stimulating light, and the predetermined frequency. A modulation unit that intensity-modulates the stimulus light with a modulation signal including The optical system that guides the light toward the object to be measured and guides the reflected light or transmitted light from the object to be measured toward the light detector, and the phase delay of the detection signal with respect to the modulated signal is detected, and the phase delay is It is provided with an analysis unit for obtaining a frequency to be a predetermined value and estimating the impurity concentration of the object to be measured based on the frequency.

According to any of the above forms, the measurement object and the stimulus light intensity-modulated with the modulation signal including the predetermined frequency are applied to the measurement object, and the intensity of the reflected light or the transmitted light from the measurement object is detected. The impurity concentration of the measurement target is estimated based on the detection signal output as a result. At this time, the frequency at which the phase delay becomes a predetermined value is estimated based on the phase delay of the detected signal with respect to the modulated signal, and the impurity concentration is estimated based on that. Therefore, even if the impurity concentration is unknown, the carrier Impurity concentration corresponding to the lifetime can be measured accurately.

In the above aspect, in the estimation step, a plurality of phase delays at a plurality of predetermined frequencies are detected, and a frequency at which the phase delay becomes a predetermined value is obtained based on a plurality of phase delays for each of the plurality of predetermined frequencies. Suitable. In the above other form, the analysis unit detects a plurality of phase delays at a plurality of predetermined frequencies, and obtains a frequency at which the phase delay becomes a predetermined value based on a plurality of phase delays for each of the plurality of predetermined frequencies. Is preferable. In this case, even when the impurity concentration is unknown, the frequency of the stimulating light that causes a phase delay of a predetermined value corresponding to the impurity concentration can be set. As a result, even when the impurity concentration is unknown, the impurity concentration can be measured accurately.

Further, in the irradiation step, it is also preferable to irradiate the stimulating light intensity-modulated by the modulated signal which is a square wave. It is also preferable that the modulation unit intensity-modulates the stimulation light with a modulation signal that is a rectangular wave. According to such a configuration, the frequency of the stimulating light that causes a phase delay of a predetermined value corresponding to the impurity concentration can be efficiently set. As a result, the impurity concentration can be efficiently measured even when the impurity concentration is unknown.

Further, it is also preferable that the irradiation step irradiates the stimulus light intensity-modulated with the modulation signals for each of the plurality of predetermined frequencies, and the output step outputs the detection signal corresponding to each stimulus light. .. It is also preferable that the modulation unit intensity-modulates the stimulus light with the modulation signal for each of the plurality of predetermined frequencies, and the photodetector outputs the detection signal corresponding to each stimulus light. In this case, even when the impurity concentration changes in a wide range, the frequency of the stimulating light that causes a phase delay of a predetermined value corresponding to the change can be set. As a result, the impurity concentration can be measured accurately even when the impurity concentration changes over a wide range.

It is also preferable to estimate the frequency at which the phase delay of the detected signal is 45 degrees. In this case, the impurity concentration can be measured more accurately by specifying the cutoff frequency.

Furthermore, in the irradiation step, it is also preferable to irradiate the stimulating light having an energy higher than the bandgap energy of the semiconductor constituting the measurement object. It is also preferable that the second light source produces stimulating light having an energy higher than the bandgap energy of the semiconductor constituting the measurement object. According to such a configuration, carriers can be efficiently generated in the object to be measured by irradiation with stimulating light, and the impurity concentration can be measured more accurately.

Further, in the above aspect, it is also preferable to further include a comparison step for comparing the information of the impurity concentration input in advance with the impurity concentration estimated in the estimation step. It is also preferable that the analysis unit compares the information on the impurity concentration input in advance with the estimated impurity concentration. By adopting such a configuration, it is possible to determine whether or not the impurity concentration in the measurement object is a desired concentration, and for example, monitoring during the manufacturing process can be realized.

Further, in the estimation step, it is also preferable to map the estimated impurity concentration to generate image data showing the distribution of the impurity concentration. It is also preferable that the analysis unit maps the estimated impurity concentration to generate image data showing the distribution of the impurity concentration. In this case, the distribution of the impurity concentration in the object to be measured can be easily measured, and the object to be measured such as a semiconductor substrate can be easily analyzed.

According to one aspect of the present invention, the impurity concentration in the object to be measured can be measured with high accuracy.

It is a schematic block diagram of the concentration measuring apparatus 1 which concerns on embodiment. It is a block diagram which shows the functional structure of the controller 37 of FIG. It is a figure which looked at the irradiation state of the measurement light and the stimulus light in DUT 10 from the direction perpendicular to the optical axis of the measurement light and the stimulus light. It is a figure which looked at the irradiation state of the measurement light and the stimulus light in DUT 10 from the direction perpendicular to the optical axis of the measurement light and the stimulus light. It is a figure which shows the waveform of the time change of a stimulus light and a detection signal generated by a concentration measuring apparatus 1. It is a graph which shows an example of the correspondence relationship between the frequency and the phase lag represented by the data stored in advance in the controller 37 of FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description, the same reference numerals are used for the same elements or elements having the same function, and duplicate explanations will be omitted.

FIG. 1 is a schematic configuration diagram of a concentration measuring device 1 according to an embodiment. The concentration measuring device 1 shown in FIG. 1 measures the concentration of impurities and the like in the DUT 10 by performing optical measurement on the device under test (DUT: Device Under Test) 10 which is an object to be measured such as a semiconductor device. It is a device of. Examples of the measurement target of the concentration measuring device 1 include a bare wafer, a substrate epitaxially grown at a constant doping density, a wafer substrate having a well or a diffusion region formed therein, a semiconductor substrate having a circuit element such as a transistor formed therein, and the like.

The concentration measuring device 1 includes a stage 3 in which the DUT 10 is arranged, a light irradiation / light guide system (optical system) 5 that irradiates and guides light toward the DUT 10 and guides the reflected light from the DUT 10. It is composed of a control system 7 that controls the light irradiation / light guide system 5 and detects and processes the reflected light from the DUT 10. The stage 3 is a support portion that supports the DUT 10 so as to face the light irradiation / light guide system 5. The stage 3 may be provided with a moving mechanism that allows the DUT 10 to move relative to the light irradiation / light guide system 5. In FIG. 1, the traveling path of light is indicated by a alternate long and short dash line, and the transmission path of a control signal, the detection signal, and the processing data are indicated by solid arrows.

The light irradiation / light guide system 5 includes a light source (first light source) 9a, a light source (second light source) 9b, collimators 11a and 11b, a dichroic mirror 13, a polarizing beam splitter 15, a 1/4 wavelength plate 17, and a galvano mirror. 19, pupil projection lens 21, objective lens 23, optical filter 25, and collimator 27 are included.

The light source 9a generates and emits light having a wavelength and intensity suitable for detecting optical characteristics that change according to the density in the DUT 10 as measurement light (probe light). The light source 9b generates and emits light including a wavelength component partially absorbed by the DUT 10 as stimulating light (pump light). Specifically, the light source 9b is set to generate stimulating light having a wavelength corresponding to an energy higher than the bandgap energy of the semiconductor which is the material of the substrate constituting the DUT 10. Further, the light source 9b is configured to be capable of generating intensity-modulated stimulating light based on an electric signal from the outside. The light source 9a and the light source 9b may be a coherent light source such as a semiconductor laser, or may be an incoherent light source such as an SLD (Super Luminescent Diode).

The collimators 11a and 11b collimate the light emitted from the light sources 9a and 9b, respectively, and the dichroic mirror 13 coaxially synthesizes the collimated measurement light and the stimulation light and outputs them to the polarizing beam splitter 15. .. The polarized beam splitter 15 transmits the linearly polarized component of the synthesized measurement light and the stimulating light, and the 1/4 wavelength plate 17 changes the polarization state of the measured light and the stimulating light transmitted through the polarized beam splitter 15. Then, the polarization state of the measurement light and the stimulation light is set to circular polarization. The galvano mirror 19 scans and outputs the circularly polarized measurement light and the stimulus light, and the pupil projection lens 21 outputs the pupil of the measurement light and the stimulus light output from the galvano mirror 19 to the objective lens from the galvano mirror 19. Relay up to 23 pupils. The objective lens 23 collects the measurement light and the stimulation light on the DUT 10. With such a configuration, the synthesized measurement light and stimulation light can be scanned and irradiated at a desired position on the DUT 10. Further, by moving the stage 3, the measurement light and the stimulus light may be able to be scanned in a range that cannot be covered by the galvano mirror 19.

Further, in the light irradiation / light guide system 5 having the above configuration, the reflected light from the DUT 10 can be guided to the 1/4 wave plate 17 coaxially with the measurement light and the stimulation light, and the 1/4 wave plate 17 can be guided. The polarization state of the reflected light can be changed from circular polarization to linear polarization. Further, the linearly polarized reflected light is reflected by the polarization beam splitter 15 toward the optical filter 25 and the collimator 27. The optical filter 25 is configured to transmit only the wavelength component of the reflected light having the same wavelength as the measured light toward the collimeter 27 and block the wavelength component of the reflected light having the same wavelength as the stimulating light. The collimator 27 collimates the reflected light and outputs the reflected light to the control system 7 via an optical fiber or the like.

The control system 7 includes a photodetector 29, an amplifier 31, a modulation signal source (modulation unit) 33, a network analyzer 35 (analysis unit), a controller (analysis unit) 37, and a laser scan controller 39.

The photodetector 29 is a photodetector such as a PD (Photodiode), APD (Avalanche Photodiode), photoelectron multiplier tube, etc., and receives the reflected light guided by the light irradiation / light guide system 5 and the reflected light thereof. Detects the intensity of light and outputs a detection signal. The amplifier 31 amplifies the detection signal output from the photodetector 29 and outputs it to the network analyzer 35. The modulation signal source 33 generates an electric signal (modulation signal) having a waveform set by the controller 37, and controls the light source 9b so as to intensity-modulate the stimulation light based on the electric signal. Specifically, the modulation signal source 33 generates an electric signal of a rectangular wave having a set repetition frequency (default frequency), and controls the light source 9b based on the electric signal. Further, the modulated signal source 33 also has a function of repeatedly generating an electric signal of a rectangular wave having a plurality of repeating frequencies.

The network analyzer 35 extracts and detects a detection signal of a wavelength component corresponding to the repetition frequency based on the detection signal output from the amplifier 31 and the repetition frequency set by the modulation signal source 33. Specifically, the network analyzer 35 extracts a detection signal having the same frequency as the repetition frequency and a detection signal having a harmonic frequency thereof. Further, the network analyzer 35 detects the phase delay of the detection signal at each frequency with respect to the intensity-modulated stimulus light based on the electric signal generated by the modulation signal source 33. Then, the network analyzer 35 inputs the information of each frequency of the extracted detection signal to the controller 37 in association with the information of the phase lag detected for the detected signal. At this time, the network analyzer 35 may repeatedly extract a detection signal for an electric signal having a plurality of repetition frequencies repeatedly set by the controller 37, and detect a phase delay for the detection signal. For example, the repetition frequency may be changed to 1/10 times, 10 times, ..., Etc. from the fundamental frequency to detect the phase delay. Here, the network analyzer 35 may be changed to a spectrum analyzer, a lock-in amplifier, or a configuration in which a digitizer and an FFT analyzer are combined.

The controller 37 is a device that comprehensively controls the operation of the control system 7, and is physically a CPU (Central Processing Unit) that is a processor, and a RAM (Random Access Memory) and a ROM (Read Only) that are recording media. Memory), a communication module, and a control device such as a computer including an input / output device such as a display, a mouse, and a keyboard. FIG. 2 shows the functional configuration of the controller 37. As shown in FIG. 2, the controller 37 includes a modulation control unit 41, a movement control unit 43, a scan control unit 45, a concentration estimation unit 47, and an output unit 49 as functional components.

The modulation control unit 41 of the controller 37 sets the waveform of the electric signal for intensity-modulating the stimulation light. Specifically, the modulation control unit 41 sets the waveform of the electric signal to be a rectangular wave having a predetermined repetition frequency. This "predetermined repetition frequency" may be a frequency having a value stored in the controller 37 in advance according to the assumed concentration of impurities or the like in the DUT 10, or is input from the outside via an input / output device. It may be the frequency of the value. Further, the modulation control unit 41 may be capable of repeatedly changing the repetition frequency from a fundamental frequency recorded or input in advance to a plurality of frequencies and setting an electric signal at the changed repetition frequency.

The movement control unit 43 and the scan control unit 45 control the stage 3 and the galvano mirror 19 so as to scan the measurement light and the stimulation light on the DUT 10. At this time, the movement control unit 43 controls to scan the measurement light and the stimulus light while performing the concentration estimation process described later for each part of the DUT 10.

The concentration estimation unit 47 executes a concentration estimation process for estimating the concentration of impurities and the like at each location of the DUT 10 based on the phase delay information for each frequency of the detection signal output from the network analyzer 35 (concentration estimation unit 47). Details of the estimation process will be described later). The output unit 49 maps the density value of each part of the DUT 10 estimated by the density estimation unit 47 on the image to generate an output image showing the distribution of the density of impurities and the like, and the input / output device of the output image. Output to.

The phenomenon measured by the concentration measuring device 1 having the above configuration will be described. 3 and 4 are views of the irradiation state of the measurement light and the stimulus light in the DUT 10 as viewed from a direction perpendicular to the optical axis of the measurement light and the stimulus light.

The light irradiation / light guide system 5 irradiates the DUT 10 with stimulating light containing a wavelength corresponding to energy higher than the band gap energy while being intensity-modulated, and at the same time, irradiates the DUT 10 with measurement light of another wavelength at a constant intensity. To. At this time, carriers are generated in the DUT 10 by the stimulating light, and these carriers disappear by recombination at a rate depending on the impurity concentration and the defect concentration in the DUT 10 at the timing when the intensity of the stimulating light is weakened.

The refractive index and transmittance in the DUT 10 are affected by the carrier density inside the substrate of the DUT 10. Due to this effect, when the measurement light is reflected on the front surface of the substrate or the back surface of the substrate, it is modulated depending on the modulation state of the stimulating light. The state of modulation of the measurement light changes according to the recombination rate of the carriers. That is, the recombination is high in the region where the concentration is high in the substrate, and is low in the region where the concentration is low. As a result, in the reflected light generated by the reflection of the measurement light, the amplitude becomes large when the recombination is high speed, while the amplitude becomes small when the recombination is low speed, and at the same time, the phase is delayed with respect to the stimulating light.

FIG. 3 shows a case where the surface of the substrate of the DUT 10 on the light irradiation / light guide system 5 side is set to irradiate the combined light L1 of the measurement light and the stimulation light. In this case, the stimulating light produces a large amount of electron-hole pairs near the surface of the substrate. Since the DUT 10 has a certain impurity concentration when it is a semiconductor substrate, there are a certain amount of a large number of carriers (electrons in the case of an n-type substrate and holes in the case of a p-type substrate) according to the impurity concentration, and a minority carrier (a minority carrier (in the case of a p-type substrate). Holes are also present in the case of n-type substrates, and electrons are also present in the case of p-type substrates. When the stimulating light is incident in this state, the refractive index of the substrate changes because the carriers are excessively present in the incident region. The reflectance R between the atmosphere and the substrate is expressed by the following equation, where the refractive index in the atmosphere is "1" and the refractive index of the substrate is n;
R = ((n-1) / (n + 1)) ²
It is known to be represented by. As the refractive index n changes due to the generation and disappearance of carriers, the reflectance R also changes, and the reflected light is modulated.

On the other hand, FIG. 4 shows a case where the light irradiation / light guide system 5 on the substrate of the DUT 10 is set to transmit the combined light L1 of the measurement light and the stimulation light to irradiate the back surface on the opposite side. .. In this case, in addition to the influence of the carrier on the reflective surface in the case of FIG. 3, the influence of the carrier in the optical path is also affected. Specifically, the carriers in the optical path cause the effect of light attenuation in addition to the change in the refractive index, so that the reflected light is affected by both. Excess minority carriers disappear at a rate proportional to the product of the density of the majority carriers, that is, the density of impurities in the substrate and the density of the excess minority carriers (more precisely, the excess minority carriers are the excess amount, Decreases at a rate proportional to the difference to the product of multiple carriers.) As a result, when the stimulating light is reduced, the refractive index returns to its original value at a rate proportional to the impurity concentration of the substrate. However, this change in the refractive index is considerably smaller than the magnitude of the refractive index of the substrate itself.

When observing the reflected light in the case shown in FIG. 3 or 4, the intensity of the reflected light changes almost corresponding to the change of the refractive index, and the time constant of the change of the reflected light with respect to the change of the stimulating light is the impurity concentration of the substrate. Inversely proportional.

FIG. 5 shows the waveform of the time change of the stimulation light irradiated by the concentration measuring device 1 in the part (a), and the stimulation light of the waveform shown in the part (a) in the parts (b) to (d). The waveform of the time change of the detection signal detected by the concentration measuring device 1 is shown. When the cycle T ₀ of the repetition of the stimulus light is considerably large (the repetition frequency is low) compared to the time constant of the change of the reflected light, the sensitivity of the phase delay observed in the detection signal as shown in part (b). Will be low. When the time constant of the change of the reflected light is about half of the cycle T ₀ of the repetition of the stimulating light (the time constant is relatively large and the phase delay is about 90 degrees), the phase in the detection signal is shown in part (c). The delay appears in the change in amplitude. In the detection signal, the phase delay most appears in the change in amplitude, as shown in part (d), the time constant of the change in the reflected light is about 1/4 of the cycle T ₀ of the repetition of the stimulating light (phase delay is 45). Degree).

In the present embodiment, the concentration is estimated by specifying the frequency of the detection signal that causes a predetermined phase delay according to the concentration of impurities and the like in the DUT 10. Here, since the rectangular wave includes the frequency component of the harmonic in addition to the frequency component of the repetition frequency, the concentration can be estimated efficiently. Further, even when the concentration in DUT 10 is unknown, the concentration can be estimated by repeatedly changing the frequency and detecting the detection signal.

Hereinafter, the details of the concentration measurement procedure including the concentration estimation process in the concentration measuring device 1 will be described.

First, the DUT 10 is placed on the stage 3. When the DUT 10 is a bare wafer, an epitaxially grown substrate, a well, a wafer substrate having a diffusion region, or the like, the DUT 10 is placed so that the measurement light and the stimulating light can be irradiated from the surface side of the substrate. In the case of a semiconductor substrate on which a circuit element is formed, it is placed so that measurement light and stimulation light can be irradiated from the back surface side of the substrate. When irradiating from the back surface side, the back surface may be polished as necessary and a solid immersion lens may be used.

After that, the measurement light and the stimulation light are irradiated from the light irradiation / light guide system 5 toward the DUT 10. At this time, the optical axis and the depth of focus of the measurement light and the stimulation light are set in advance so as to be the same, and the light irradiation / light guide system 5 is an optical system having sufficiently small chromatic aberration. At this time, the angle of the front surface or the back surface of the DUT 10 is adjusted so as to be perpendicular to the optical axis of the measurement light and the stimulation light, and the focal point of the measurement light and the stimulation light is also set to match the measurement surface of the DUT 10.

Further, the control of the controller 37 is controlled so that the stimulation light is intensity-modulated by the rectangular wave. The repetition frequency of this square wave is preset according to the assumed impurity concentration, and is set to about 1 kHz if the impurity concentration is on the order of 10 ¹⁵ / ^cm3 . For impurity concentrations of other values, the repeat frequency is set in proportion to the expected concentration.

Next, in the photodetector 29 of the control system 7, the reflected light from the measurement surface of the DUT 10 is detected to generate a detection signal, and the detection signal is amplified by the amplifier 31. Then, the network analyzer 35 of the control system 7 extracts the repeating frequency component and the harmonic component thereof from the detection signal. At this time, the bandwidth is set so as to avoid 0 Hz ground noise.

In addition, the network analyzer 35 of the control system 7 detects a phase delay with respect to the modulated signal of the stimulating light for the waveforms of the extracted detection signals of a plurality of frequencies. Further, the network analyzer 35 outputs to the controller 37 the corresponding data in which the information on each frequency of the extracted detection signal and the information on the phase lag detected on the detected signal are associated with each other.

The detection of the phase lag of the detection signals having a plurality of frequencies and the output of the corresponding data related thereto may be repeatedly performed for a plurality of repeating frequencies set repeatedly. This makes it possible to estimate the concentration even when the concentration of impurities or the like is unknown. Further, the detection of the phase lag of the detection signals having the plurality of frequencies and the output of the corresponding data related thereto are repeatedly performed while scanning the measurement points on the DUT 10 under the control of the controller 37.

After that, the controller 37 estimates the concentration of impurities and the like at the plurality of measurement points using the corresponding data regarding the plurality of measurement points on the DUT 10 (concentration estimation process). That is, a frequency at which the phase delay becomes a predetermined value is estimated, and the concentration of impurities or the like at the measurement point on the DUT 10 is estimated based on the frequency. At this time, if the frequency that causes a predetermined phase delay cannot be estimated, the frequency may be further changed and the reflected light detection process may be repeated.

More specifically, the frequency at which the phase lag is 45 degrees is estimated based on the phase lag values of the detection signals of a plurality of frequencies. This frequency is called the cutoff frequency, and the time constant τ at this time is 1 / (2π) times the period corresponding to this frequency. This time constant τ corresponds to the carrier lifetime inside the DUT 10. In general, the carrier lifetime τ is expressed by the following equation, where B is a proportional constant, p ₀ is a majority carrier concentration (= impurity concentration), n ₀ is a minority carrier concentration, and Δ n is an excess carrier concentration;
τ = 1 / {B (n ₀ + p ₀ + Δn)} to 1 / (B · p ₀ )
It is represented by. Utilizing this property, the controller 37 calculates the carrier lifetime τ from the frequency at which the phase delay is 45 degrees, and estimates the impurity concentration (= p ₀ ) from the carrier lifetime τ by back-calculating the above equation. Calculate as.

Here, when estimating the frequency at which the phase delay is 45 degrees based on the phase delay values of the detection signals of a plurality of frequencies, it is not always necessary to extract the detection signal whose phase delay matches 45 degrees. A frequency having a phase lag of 45 degrees may be obtained by analytical calculation such as curve fitting based on the generated corresponding data. In this case, the controller 37 stores data indicating the correspondence between the frequency and the phase lag in advance, and the combination of the frequency of the detection signal and the measured value of the phase lag is fitted into the correspondence relationship stored in advance. The frequency at which the phase delay is 45 degrees is estimated. FIG. 6 shows an example of the correspondence between the frequency represented by the data stored in advance in the controller 37 and the phase lag (the frequency on the horizontal axis is a frequency having the cutoff frequency as a unit).

Finally, the controller 37 maps the estimated density values for the plurality of measurement points onto the image to generate data for the output image showing the density distribution on the DUT 10. Then, the output image is output to the input / output device based on the data. With this output image, a fine density distribution on the DUT 10 can be observed in a non-contact manner and with a high dynamic range. For example, spots of impurity concentration can be easily observed. In addition, spots in heat dissipation characteristics on the DUT 10 can be measured at the same time.

According to the concentration measuring device 1 described above and the concentration measuring method using the same, the DUT 10 is simultaneously irradiated with the measured light and the stimulating light intensity-modulated by the modulation signal including the predetermined frequency, and the intensity of the reflected light from the DUT 10 is increased. Is detected, and the impurity concentration of the DUT 10 is estimated based on the detection signal output as a result. At this time, the frequency at which the phase delay becomes a predetermined value is estimated based on the phase delay of the detected signal with respect to the modulated signal, and the impurity concentration is estimated based on that. Therefore, even if the impurity concentration is unknown, the carrier Impurity concentration corresponding to the lifetime can be measured accurately.

Further, in the present embodiment, a plurality of phase delays at a plurality of predetermined frequencies are detected, and a frequency at which the phase delay becomes a predetermined value is estimated based on a plurality of phase delays for each of the plurality of predetermined frequencies. In this case, even when the impurity concentration is unknown, the frequency of the stimulating light that causes a phase delay of a predetermined value corresponding to the impurity concentration can be set. As a result, even when the impurity concentration is unknown, the impurity concentration can be measured accurately.

Further, in the present embodiment, the frequency at which the phase delay of the detection signal is 45 degrees is estimated. By doing so, the impurity concentration can be measured more accurately based on the cutoff frequency.

Further, in the present embodiment, the stimulation light is intensity-modulated with a plurality of modulation signals for each predetermined frequency, and a detection signal is generated corresponding to each stimulation light. By doing so, even when the impurity concentration changes in a wide range, it is possible to set the frequency of the stimulating light that causes a phase delay of a predetermined value corresponding to the change. As a result, the impurity concentration can be measured accurately even when the impurity concentration changes over a wide range.

Further, in the present embodiment, a stimulating light whose intensity is modulated by a rectangular wave is used. With such a configuration, it is possible to easily acquire the phase lag in the detection signals having a plurality of frequencies. As a result, the frequency of the stimulating light that causes a phase delay of a predetermined value corresponding to the impurity concentration can be efficiently set, so that the impurity concentration can be efficiently measured even when the impurity concentration is unknown. Can be done.

Further, in the present embodiment, stimulating light having an energy higher than the bandgap energy of the semiconductor constituting the DUT 10 is used. With such a configuration, carriers can be efficiently generated in the DUT 10, and the impurity concentration can be measured more accurately.

Although various embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and the gist described in each claim is modified or applied to other embodiments without modification. It may be a thing.

As the DUT 10 to be measured in the above embodiment, a semiconductor substrate in which impurities are diffused in the manufacturing process of a semiconductor device such as an LSI may be selected. When performing concentration measurement on such a semiconductor substrate, a measurement point, which is a measurement target point of the DUT 10, is set in advance in the controller 37, and light irradiation / guidance is performed so as to scan the measurement point. System 5 is controlled. In addition, information on the expected impurity concentration is input to the controller 37 in advance via the input / output device. Then, the controller 37 compares the numerical value of the impurity concentration estimated with respect to the measurement point with the information of the impurity concentration input in advance, and determines whether or not the comparison result (for example, whether or not they match within a predetermined error range). The result) is output to the input / output device. In such a configuration, it is possible to determine whether or not the diffusion region is appropriately generated in the manufacturing process of the semiconductor device.

The light irradiation / light guide system 5 of the above embodiment is configured to be able to guide the reflected light from the DUT 10 toward the control system 7, but controls the transmitted light generated by the measured light passing through the DUT 10. It may be configured to be able to guide light toward the system 7. In this case, the density is estimated based on the detection signal generated by detecting the transmitted light in the control system 7.

The light irradiation / light guide system 5 of the above embodiment may be provided with a fiber coupler instead of the dichroic mirror 13 or may be provided with a fiber having a plurality of cores as an element for synthesizing the measurement light and the stimulation light. ..

In the light irradiation / light guide system 5 of the above embodiment, the polarization beam splitter 15 may be arranged between the dichroic mirror 13 and the light source 9a. In this case, the dichroic mirror 13 serves as an optical filter 25.

In the light irradiation / light guide system 5 of the above embodiment, the optical axis and the focal point are aligned between the measurement light and the stimulation light, but the spot of the stimulation light at the measurement point of the DUT 10 is the measurement light. It does not necessarily have to be in focus as long as it includes the spots of. Further, when a fiber having a plurality of cores is used, the optical axis may be offset between the measurement light and the stimulation light.

Further, in the above embodiment, if the photodetector 29 is configured to have sensitivity only to the measurement light, the optical filter 25 may be omitted.

Further, in the above embodiment, the measurement is performed using the stimulus light intensity-modulated with a square wave, but a plurality of stimuli corresponding to a plurality of frequencies, which are intensity-modulated with signals of other waveforms such as a sine wave. Light may be used.

1 ... concentration measuring device, 5 ... light irradiation / light guide system (optical system), 7 ... control system, 9a ... light source (first light source), 9b ... light source (second light source), 29 ... light detector, 33 ... Modulation signal source (modulation unit), 35 ... Network analyzer (analysis unit), 37 ... Controller (analysis unit).

Claims (16)

It is a concentration measurement method that measures the impurity concentration of the object to be measured.
An irradiation step of irradiating the measurement object with the measurement light and the stimulation light intensity-modulated with the modulation signal including the predetermined frequency.
An output step that detects the intensity of reflected light or transmitted light from the measurement object and outputs a detection signal.
An estimation step of detecting the phase delay of the detected signal with respect to the modulated signal, obtaining a frequency at which the phase delay becomes a predetermined value, and estimating the impurity concentration of the measurement object based on the frequency.
Concentration measurement method. In the estimation step, a plurality of the phase delays at the plurality of predetermined frequencies are detected, and a frequency at which the phase delay becomes a predetermined value is obtained based on the plurality of phase delays for each of the plurality of predetermined frequencies.
The concentration measuring method according to claim 1. In the irradiation step, the stimulating light intensity-modulated by the modulated signal which is a square wave is irradiated.
The concentration measuring method according to claim 1 or 2. In the irradiation step, the stimulating light intensity-modulated with the modulation signals for each of the plurality of predetermined frequencies is irradiated.
In the output step, the detection signal is output corresponding to each stimulus light.
The concentration measuring method according to claim 2. The predetermined value is 45 degrees.
The concentration measuring method according to any one of claims 1 to 4. In the irradiation step, stimulation light having an energy higher than the bandgap energy of the semiconductor constituting the measurement object is irradiated.
The concentration measuring method according to any one of claims 1 to 5. Further provided, a comparison step of comparing the information of the impurity concentration input in advance with the impurity concentration estimated in the estimation step is provided.
The concentration measuring method according to any one of claims 1 to 6. In the estimation step, the estimated impurity concentration is mapped to generate image data showing the distribution of the impurity concentration.
The concentration measuring method according to any one of claims 1 to 7. A concentration measuring device that measures the concentration of impurities in an object to be measured.
The first light source that produces the measurement light and
A second light source that produces stimulating light,
A modulation unit that intensity-modulates the stimulus light with a modulation signal including a predetermined frequency,
A photodetector that detects the intensity of reflected light or transmitted light from the object to be measured and outputs a detection signal.
An optical system that guides the measurement light and the intensity-modulated stimulus light toward the measurement object, and guides the reflected light or transmitted light from the measurement object toward the light detector.
An analysis unit that detects the phase delay of the detected signal with respect to the modulated signal, obtains a frequency at which the phase delay becomes a predetermined value, and estimates the impurity concentration of the measurement object based on the frequency.
Concentration measuring device. The analysis unit detects a plurality of the phase lags at the plurality of the predetermined frequencies, and obtains a frequency at which the phase lag becomes a predetermined value based on the plurality of phase lags for each of the plurality of predetermined frequencies.
The concentration measuring device according to claim 9. The modulation unit intensity-modulates the stimulation light with the modulation signal which is a rectangular wave.
The concentration measuring device according to claim 9 or 10. The modulation unit intensity-modulates the stimulation light with the modulation signals for each of the plurality of predetermined frequencies.
The photodetector outputs the detection signal corresponding to each stimulus light.
The concentration measuring device according to claim 10. The predetermined value is 45 degrees.
The concentration measuring device according to any one of claims 9 to 12. The second light source produces stimulating light having an energy higher than the bandgap energy of the semiconductor constituting the measurement object.
The concentration measuring device according to any one of claims 9 to 13. The analysis unit compares the information of the impurity concentration input in advance with the estimated impurity concentration.
The concentration measuring device according to any one of claims 9 to 14. The analysis unit maps the estimated impurity concentration and generates image data showing the distribution of the impurity concentration.
The concentration measuring device according to any one of claims 9 to 15.

Images